1. Field of the Invention
This invention relates to machine tools; more particularly, it relates to a mechanism for driving the axis of a rotative spindle along a programmed path.
2. Description of the Prior Art
There are many applications in the machining of metals and other materials wherein it is desirable to move a tool along a programmed path other than or in addition to rotation about its own axis and rectilinear displacement along that axis or normal thereto. In particular, there are applications in which it is desired to rotate a cutting tool about its own axis while it is fed longitudinally of its axis, in the manner of a drill or end mill as in a simple drilling operation and, to compound the tool motion by moving the tool axis in an orbital path during tool rotation and axial feed, as in the case of milling threads in a drilled hole. Such a tool spindle driver is especially useful in high speed machining; for example, in making a hole on the inward feed of the tool and milling threads therein on the continued inward feed or the outward feed of the tool. A special tool adapted for combined hole making and thread making with a single spindle is disclosed and claimed in copending application Ser. No. 840,443 entitled "COMBINED HOLE MAKING AND THREADING TOOL" filed Mar. 17, 1986 by Manuel C. Turchan. In general, there are many applications in the use of machine tools for a spindle driver which can impart helical motion to a tool either with or without rotation of the tool about the tool axis. For general applications of this kind, it is desired to provide a helical motion of variable pitch and variable diameter.
The prior art includes apparatus for milling internal threads in a bore in a workpiece. Apparatus of this kind is described in Miller et al 2,526,762 granted Oct. 24, 1950. The miller et al patent describes a machine in which a tubular workpiece is mounted for revolution in a fixed longitudinal position with machine elements carrying threading hobs positioned eccentrically of the workpiece in cutting engagement with the internal periphery thereof and mounted for longitudinal movement relative to the workpiece as the revolution of the workpiece progresses. The Miller et al patent also describes a machine in which the threading hob is longitudinally fixed and the workpiece is moved longitudinally during revolving motion thereof for cutting the threads.
The Escobedo Pat. No. 3,526,167 granted Sept. 1, 1970 describes a milling head for driving a rotary cutting tool in a predetermined path such as a spiral path. A fixed paper upper housing is mounted on the quill of a milling machine and a manually rotatable lower housing is connected therewith by a pair of telescopic tubes. Within the inner telescopic tube, an internally threaded guide cylinder is mounted on the fixed upper housing and an externally threaded guide cylinder engages the first guide cylinder and is attached to the rotatable lower housing. The spindle of the milling machine is coupled with the rotary drive shaft which extends coaxially of the guide members and carries a drive gear in the lower housing. A driven gear is mounted on a driven spindle having a tool socket adapted to receive a shank of a cutting tool. An intermediate gear engages both the drive and driven gear and transmits rotary motion therebetween. A transverse guideway in the lower housing contains a slide block which is pivoted on a stub shaft carrying the intermediate gear. The slide block can be pivoted so that the driven gear is aligned or selectively misaligned with the driving gear. This positioning of the slide block allows the driven spindle to be positioned coaxially of the driving spindle or to be adjustably positioned eccentrically of the driving spindle.
The Lanzenberger Pat. No. 3,105,413 granted Oct. 1, 1963 discloses a machine tool for milling or grinding a cylindrical or conical bore. In this machine tool, a main spindle carries a tool holder which is rotationally driven by the main spindle about the main spindle axis. A grinding tool carried by the tool holder has its own driving means such as a pneumatic turbine. The rotational axis of the grinding tool is shifted relative to the main spindle axis by means of a cam disposed within the main spindle. The main spindle is disposed for rotation within a spindle support which carries the tool holder at the lower end. The tool holder is rotatably driven by the main spindle and it is moved axially by a spindle support sleeve which is driven by an external driving member. A crank lever is moved with respect to the spindle support sleeve and imparts axial movement to an inner spindle which engages the cam for adjusting the offset of the axis of the spindle of the grinding tool from the axis of the main spindle.
The Hoddinott et al Pat. No. 3,859,001 granted Jan. 7, 1975 discloses a mechanism for driving a quill in the tool head of a machine tool. In this apparatus, the quill carries a rotatable spindle which drives a working tool. The quill is held against rotation and is advanced and retracted relative to the workpiece by a ball screw.
The Kratchman Pat. No. 2,451,497 granted Oct. 19, 1948 discloses a thread miller adapted for milling internal threads. An inner housing has a cylindrical upper portion which is coupled with a power shaft and has a lower portion with an eccentric cylindrical internal shaftway therein. An eccentric bushing has a driven shaft journalled therein and the bushing is rotatable within the eccentric shaftway of the inner housing. A coupling shuttle connects the drive shaft to the driven shaft and a milling cutter is mounted on the driven shaft. Means are connected to the eccentric bushing for rotating it and thus varying the eccentricity of the milling cutter. The inner housing is provided with external threads which coact with the threads of a rotatable, axially fixed nut in the manner of a lead screw for spirally moving the inner housing to cause the milling cutter to mill a thread in a drilled hole.
The Zorich Pat. No. 2,742,796 granted Apr. 24, 1956 discloses an adjustable drill holder for use in drilling eccentric holes. A driving shaft is journalled eccentrically in a holder which is secured in a bore in the turret of a machine tool. A driving shaft is connected through gearing to a spindle which carries a collet for a drill. The spindle is journalled in a rotatable head and is eccentric from the axis of the holder. By adjusting the holder about its axis and by adjusting the head about its axis, the offset or eccentricity of the drill can be varied from zero up to a predetermined distance from the axis of the holder.
It is known to use lead screws for advancing and retracting a spindle of a machine tool, as described in Kratchman Pat. No. 2,451,497 cited above. It is also known in the prior art to utilize a differential lead screw for positioning of robot arms and the like. A differential lead screw for this purpose is available from Robomatix, Limited of Israel and is illustrated in an undated leaflet entitled "LIGHTWEIGHT ROLL AND Z AXIS UNIT FOR HORIZONTAL TYPE ROBOT ARMS".
A general object of this invention is to provide an improved spindle driver for imparting helical motion to a rotating tool with controllable pitch in a mechanism which overcomes certain disadvantages of the prior art.